The world's computing infrastructure is increasingly differentiating into self-contained sub-systems (e.g. Internet of Things installations, clouds, VANETs, ...), which are post-hoc composed to generate value-added functionality (“systems of systems”). Today, however, such system-of-systems composition is typically carried out in an ad-hoc and infrastructure-dependent manner, with obvious associated disadvantages. In this paper, we propose a generalised system-of-systems-oriented programming approach that enables programmers to manage the composition of systems without a need for intimate knowledge of their internals, and also facilitates dynamic and spontaneous system composition, as systems discover each other opportunistically in their environment.